The circuit breaker of the kind referred to comprises, as has been disclosed in, for example, U.S. Pat. No. 3,329,913 and Japanese Patent Publication No. 18258/1966, a fixed contactor carrying a fixed contact, a movable contactor carrying a movable contact contactable with the fixed contact, a manual contact opening and closing mechanism normally operable to separate the movable contactor from the fixed contactor and including a trip means which forcibly separates the movable contactor from the fixed contactor, an electromagnetic device operating in response to the short-circuit current as well as the overcurrent to attract an armature linked to the trip means, and an arc suppressing means disposed adjacent contacting and separating position of the fixed and movable contacts.
Thus the contacts are normally closed and opened by means of the manual contact opening and closing mechanism which moves the movable contactor with respect to the fixed contactor whereas, upon the short-circuit or when the over-current higher than the rated current keeps flowing, they are opened by means of the trip means which separates the movable contactor from the fixed contactor with an actuation of the electromagnetic device and attraction of the armature. An arc generated upon such contact opening is shifted towards the arc suppressing means to be therein divided, cooled and suppressed.
In the known circuit breaker, however, a relatively long time has been required until a complete arc suppression is achieved after the separation of the movable contactor from the fixed contactor by the trip means specifically upon the actuation of the electromagnetic device due to the short-circuit current which produces the attraction of the armature. Due to that, for example, the arc suppressing means is merely disposed adjacent the contacting and separating position of the contacts, rendering the relatively long time required for driving and drawing the arc towards the arc suppressing means by a magnetic driving force and consequently until the complete arc suppression is reached, and so on, the entire device has been functionally insufficient. Accordingly, there has been a problem that, in an event where the circuit of which breaking is to be made includes such elements low in the withstand voltage as semiconductor elements, they are damaged by a high voltage applied thereto upon the short-circuit. It has been desired for the circuit breaker of the kind referred to that the movable contactor is rapidly separated from the fixed contactor specifically at the time of the actuation of the electromagnetic device responsive to the short-circuit current, and that the arc suppression is achieved in an extremely short time, so that the current limiting effect can be remarkably improved and a smooth application to the circuit involving the elements of low voltage can be achieved.